Formation Mechanism of the Changxing Formation Gas Reservoir in the Yuanba Gas Field,Sichuan Basin,China

In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and diagenetic evolution caused the Changxing Formation to form lithologic traps, with good reservoirs such as dissolved bioclastic dolostone and dissolved pore dolostone. The Changxing Formation gas reservoir is a pseudo-layered porous lithologic gas reservoir under pressure depletion drive, with high H2S and moderate CO2 contents. This paper predictes that the conducting system for the Changxing Formation gas reservoir is possibly composed of the pores and microfractures in the Changxing Formation reservoir, the top erosional surface of the Changxing Formation, as well as the micropores and microfractures in the underlying formations. The Changxing Formation reservoir has experienced 3 hydrocarbon charging stages. This paper suggests that diffusion is the major formation mechanism for this gas reservoir. In the Middle and Late Yanshanian, the Yuanba area entered the major gas charging stage. The gas migrated mainly through diffusion and with the assistance of seepage flow in small faults and microfractures from the source rocks and the other oil-bearing strata to the Changxing Formation carbonate reservoir rocks, forming lithologic gas pools. In the Himalayan Epoch, the lithologic traps were uplifted as a whole without strong modification or overlapping, and were favorable for gas preservation.

Discovery and theoretical and technical innovations of Yuanba gas field in Sichuan Basin, SW China

To solve the difficulties in exploration and development in Yuanba ultra-deep gas field in Sichuan Basin,SW China,the article studies the mechanism of quality reef reservoirs development and gas accumulation and innovates techniques in ultra-deep seismic exploration,drilling,completion and testing.Through the reconstruction of dynamic depositional evolution process and regional depositional framework of homoclinal ramp-rimmed platform in Upper Permian,three theories are put forward:first,"early beach-late reef,multiple stacking,arrangement in rows and belts"is the sedimentary mode for the reservoirs in the Changxing Formation of Yuanba area;second,"dissolution in early exposure stage and dolomitization during shallow burial giving rise to the pores in matrix,overpressure caused by cracking of liquid hydrocarbon during deep burial inducing fractures"is the reservoirs development mechanisms;third,"coupling of pores and fractures"controls the development of high quality reservoirs in deep formations.From correlation of oil and source rock,it is concluded that the Wujiaping Formation and Dalong Formation of deep-water continental shelf are the major source rocks in the Permian of northern Sichuan Basin.The hydrocarbon accumulation mode in ultra-deep formations of low-deformation zones is characterized by"three-micro(micro-fault,micro-fracture interbed crack)migration,near-source enrichment,and persistent preservation".Through seismic inversion using the pore structure parameters of pore-fracture diadactic structure model,the high production gas enrichment area in Yuanba gas field is 98.5 km^2.Moreover,special well structure and unconventional well structure were used to deal with multiple pressure systems and sealing of complex formations.A kind of integral,high pressure resistant FF-level gas wellhead and ground safety linkage device was developed to accomplish safe and environmentally friendly gas production.

Characteristics and main controlling factors of reservoirs in the fourth member of Sinian Dengying Formation in Yuanba and its peripheral area, northeastern Sichuan Basin, SW China

Based on the abundant outcrops and 3 D seismic data in Yuanba and its surrounding areas in northeastern Sichuan Basin,the characteristics,main controlling factors and development regularities of reservoirs in the fourth member of Sinian Dengying Formation(shortened as Deng 4 Member)were analyzed comprehensively.The results show that the reservoirs were mainly developed in microbial dolomite associated with the microbial mound and dolarenite associated with grain beach,and had intergranular dissolution pores,inter-frame dissolution pores and karst caves as main storage space.The reservoirs were large in scale and strong in heterogeneity.The analysis of the reservoir genetic mechanisms shows that the reservoirs in the fourth member of Dengying Formation were the products of karstification on mound-beach facies deposited in the second episode of Tongwan movement.The karstification had the marks of eogenetic karstification such as granophyric karst system and half-dissociation zone.The reservoirs were controlled by the sedimentary facies belt,the mound beach facies was the decisive factor in reservoir development.Further analysis indicates that the Yuanba area had a geological background of well-developed platform margin mound beach facies,so mound beach bodies can be taken as a favorable exploration target.

Seismic Sedimentology Study in the High-Resolution Sequence Framework——A Case Study of Platform Margin Reef-Beach System of Changxing Formation,Upper Permian,Yuanba Area,Northeast Sichuan Basin,China

The Yuanba （元坝） area is considered another potential large-scale reef-bank gas field following the Puguang （普光） field. However, there are lots of difficulties on the spatial and temporal distribution of reef-beach and the detailed prediction of the effective reservoir in the sequence stratigraphic framework. In this paper, based on the seismic data, well, log and core, we conduct a high-resolution sequence division and build an isochronal sequence stratigraphic framework for the Changxing （长兴） Formation by the methods of wavelet transformation, FMI, etc.. Then, the corresponding relationship among the lithologic facies, logging facies, seismic facies, seismic attribute facies and reservoir of Changxing Formation were established through well-seismic calibration and geological-geophysical modeling. Furthermore, detailed study on the spatial and temporal distribution of microfacies of the reef-beach was carried out by means of seismic attribute extraction. Meanwhile,combined with impedance inversion, the spatial distribution of porosity of reef-beach reservoir was predicted. The results show that the revolution of the reef-beach system contains three stages which are initial bioclastic bank establishment stage, reef development stage and exposure stage. Also, porosity inversion shows that the region with high value of porosity is located in the reef cap, fore reef and back reef.Seismic Sedimentology Study in the High-Resolution Sequence Framework

Mesozoic Tectonic Evolution and Thermal History of the Yuanba Area of Northeast Sichuan Basin-Low-Temperature Thermochronology of Apatite and Zircon

By means of the vitrinite reflectance and U-Th/He dating of apatite and zircon in cut- ting samples from the T3x-K1j formations in the Yuanba （元坝） area of Northeast Sichuan （四川） Basin, a correlation has been established between the He-derived age and depth/temperature in this area assuming helium closure temperature of apatite in this area being 95 ℃. Mesozoic strata （T3x-Kd＇） experienced helium closure temperature of apatite approaching 95 ℃, but didn＇t reach the helium closure temperature of zircon （ca. 170-190 ℃） although some reached the highest pa- laeogeothermal temperature of about 170 ℃. The Mesozoic strata in the Yuanba area experienced an important uplift and denudation during Paleogene-Neogene periods （0.2-36.4 Ma）, the erosion rate being about 109.9 m/Ma. The K1] Formation and overlying strata experienced a maximum de- nudation loss of about 4 000 m. Geotemperatures gradually fell to the helium closure temperature of apatite and then fell further to the current temperature. The thermal evolution history of this area indicates that the maximum palaeogeothermal temperature of Mesozoic strata was close to 170- 190 ℃, prior to the strata being uplifted. During the period between 176 and 36 Ma, the palaeogeo- thermal temperature fell to 95-170 ℃. and after 36 Ma, it continued to fall to the present geotem- perature of less than 95 ℃.

Characteristics and formation mechanism of Changxing Formation-Feixianguan Formation reef-shoal reservoirs in Yuanba Gasfield

Taking advantage of the successful experience in exploring and discovering the Puguang Gasfield,and targeting the Changxing Formation-Feixianguan Formation organic reef and shoal lithological trap,SINOPEC drilled Well Yuanba 1 in the Bazhong area in Northeast Sichuan in 2006,and discovered the Yuanba Gasfield with a high-production commercial gas flow of 503×10^(3) m^(3)/d.As a normal-pressured lithological gas reservoir with high H_(2)S content,Yuanba Gasfield is characterized by weak tectonic deformation and deep burial,with an average depth of 6,600 m in the central part of the gas reservoir,and is the deepest marine gas field in the Sichuan Basin.Yuanba Gasfield is dominated by large-scale reef-shoal reservoirs of Changxing Formation.The formation of the reservoirs was primarily controlled by early meteoric freshwater dissolution and dolomitization,and less affected by deep-burial dissolution and tectonic movement.A comparative analysis was made on the characteristics of deep reef-shoal reservoirs in the Yuanba and Puguang gas fields so as to explore their formation mechanisms.It is concluded that the reservoir size and early pore development was controlled by early depositional-diagenetic environment.Fracture formation and dissolution were controlled by structure-fluid coupling,pore reworking and preservation is determined by fluid-rock interaction.

Hydrocarbon accumulation conditions and key technologies for exploration and development of Yuanba gas field

This paper discusses the exploration and development history and lessons of the large ultra-deep biogenic reef gas field in Yuanba area,where the previous“Kaijiang-Liangping shelf”model provides an insight for the discovery of the biological reef and bank on the platform margin.Systematic analysis of key geological conditions for hydrocarbon accumulation shows that the reef and bank reservoirs in Yuanba area are characterized by row and zonal distribution along“Kaijiang-Liangping shelf”,the bank in early and the reef in late,the reef in the front and the bank in the back,and dominated by lateral accretion and progradation.The major exploration target of high-quality reef-bank reservoirs are developed in Changxing Formation instead of in Feixianguan Formation,Three stages of fractures and dissolution,and dolomitization control the development of the high-quality reservoirs.Two sets of effective source rocks(Permian Dalong Formation and Wujiaping Formation)provide sufficient gas source for the large gas field.Three dimensional migration pathway system composed of micro-faults,micro-fractures and interlayer fissures facilitates the hydrocarbon migration and accumulation.The accumulation model of Yuanba gas field is characterized by the near-source accumulation,three-micro migration pathway system,lithological-stratigraphic reservoirs and tectonics controlling enrichment.According to the complex geological conditions such as ultra-deep reservoirs and multiple pressure systems in Yuanba gas field,several key technologies are developed during hydrocarbon exploration and development,including fine prediction of ultra-deep reef-bank reservoirs and identification of gas and water,fine-scale reservoir description and characterization of complex thin and small reef gas reservoirs,optimal&fast drilling of ultra-deep horizontal well,geo-steering of ultra-deep horizontal well for complex reef and bank.All these technologies resulted in the efficient exploration and development of Yuanba gas field and accelerated the innovation of theoretical technology and methods for ultra-deep reservoirs.

复杂底水气藏水侵动态模拟及应用——以元坝长兴组气藏为例

元坝长兴组气藏为局部发育隔夹层的条带状生物礁底水气藏,不同气水分布模式下两相渗流机理复杂,水侵动态认识不深入,控水对策制定缺乏理论指导,严重制约了气藏高产稳产。通过设计流体微观渗流实验,分析不同气水分布模式水侵机理,建立隔层型及无隔层型气井水侵早期预警模型,开展气井见水风险评级,形成差异化控水稳气技术对策。研究成果表明:1)气藏隔层发育使得水侵机理呈现显著差异,考虑复杂气水分布模式能够有效提升水侵动态模拟精度,气井见水时间预测误差可小于10%。2)无隔层型及隔层型2类气水分布模式气井无水采气期的可控因素影响程度由强到弱均为避水高度、生产压差及井筒内径。3)针对无隔层型井区气井,避水高度对气井无水采气期影响趋势与生产压差及井筒内径有显著差异,其影响规模可达另2个因素的3倍以上;隔层型气井无水采气期对于各因素敏感性较无隔层气井显著降低,影响程度变化趋势趋于一致。4)识别气井水侵加剧特征后,应综合考虑底水锥进临界产量及产能来动态调控气井生产压差,延缓水侵速度,元坝气田产水风险井无水采气期平均延长2.3年,控水侵效果显著。以上研究成果有效支撑了元坝气田水侵动态分析及防控对策制定,为同类型气藏高效开发提供技术借鉴。

川东北元坝地区侏罗系陆相页岩天然裂缝发育特征及其对页岩油气富集和保存的影响

川东北元坝地区陆相页岩中天然裂缝发育,是影响页岩油气富集和保存的关键因素。本文依据岩心、镜下薄片和扫描电镜等资料研究该区侏罗系大安寨段和千佛崖组页岩层系天然裂缝的发育分布特征,探讨裂缝对页岩油气富集和保存的影响。结果表明,侏罗系页岩中主要发育构造裂缝、层理缝、穿层水力破裂缝和收缩缝,其中构造裂缝包括穿层剪切缝、顺层剪切缝和层内张开缝,层理缝是页岩中最为发育的天然裂缝,线密度介于66~357条/m之间,平均为188条/m。层理缝和收缩缝既是页岩油气的储集空间也是运移通道,改善了页岩的储集性能,有利于页岩油气的富集。构造裂缝、穿层水力破裂缝与层理缝相互连通形成的宏观裂缝网络是页岩油气排放的通道,对大安寨段页岩气的逸散影响较大,对千佛崖组页岩油的保存条件影响较小。研究成果可为四川盆地陆相页岩油气勘探开发提供基础性参考依据。

四川盆地元坝地区二叠系茅口组相控岩溶刻画及预测

通过岩溶古地貌恢复、倾角约束增强相干、相控岩溶地震反演和非线性伽马模拟等技术,对四川盆地元坝地区二叠系茅口组相控岩溶异常及有效储层分布进行了研究。研究结果表明:①四川盆地元坝地区二叠系茅口组在纵向上可划分为表层风化壳、垂直渗流带、水平潜流带3个岩溶作用带,茅三段相控岩溶储层受浅滩相带和岩溶作用共同控制,储层类型分为孔隙-孔洞型和半充填溶洞型。②岩溶残丘地貌相对较高,为岩溶作用供水区域,是相控岩溶发育的有利位置;溶丘平原地貌相对较低,为岩溶作用汇水区域。③倾角约束的增强相干技术可定性描述岩溶残丘内相控岩溶发育的有利带,研究区的该类储层主要分布于古地貌高部位,并呈北西向展布。④相控岩溶储层预测方法可以相对准确地预测有效岩溶储层的分布范围,研究区垄脊带、峰丛带岩溶储层最为发育,最大厚度为28m。

元深1井超深井钻井提速关键技术

元深1井是部署在川北低缓构造带上的重点探井,钻井过程中面临地层压力体系复杂、井眼易坍塌、钻井液易漏失、陆相地层研磨性强、井控风险高等技术难题。根据地质特征,借鉴邻井钻井经验,应用泡沫钻井技术,提高浅部地层大尺寸井眼机械钻速;应用“涡轮钻具+孕镶金刚石钻头”和“旋冲钻具+混合式钻头”提速技术,解决陆相高研磨性地层机械钻速低的难题;应用耐高温防漏堵漏钻井液,配套“高效PDC钻头+大扭矩螺杆”提速技术,实现海相多压力体系复杂地层安全快速钻进;用微心PDC钻头钻进目的层,在满足岩屑录井需要的同时,提高了钻井效率。该井顺利钻至井深8866.00 m完钻,创中国石化四川盆地直井井深最深纪录,为四川盆地超深井钻井积累了经验。

深层碳酸盐岩沉积微相决策树测井识别方法

深层海相碳酸盐岩储层是油气勘探开发的重要领域,沉积微相识别与划分是开展储层精细描述的基础与关键。为建立以测井资料为基础的复杂礁滩相碳酸盐岩储层沉积微相自动识别方法,以元坝长兴组礁滩相储层为例,结合常规测井、电成像测井及地质资料,明确不同微相的测井响应特征,建立涵盖不同沉积微相岩石物理与测井曲线形态差异的智能识别样本集。针对现有C4.5决策树算法在缺失属性样本分类问题中表现出的建树结构复杂、精度低等问题,提出一种基于贝叶斯原理的适用于缺失值问题的决策树新方法,降低了建树的不确定性,提高了运算效率。经7口井检验,沉积微相识别符合率达到90%以上,新方法丰富并完善了深层海相碳酸盐岩储层勘探开发技术体系,为利用测井资料开展复杂礁滩相碳酸盐岩沉积微相划分提供可靠依据。

川东北元坝地区长兴期飞仙关期碳酸盐岩台地沉积体系及演化

四川盆地东北部元坝地区二叠纪-三叠纪沉积环境主要与北部广旺海槽形成与关闭、米仓山与大巴山隆起及二叠纪峨眉山玄武岩喷发有关。通过野外露头、三维地震数据、钻井资料的综合研究,认为长兴组-飞仙关组沉积为碳酸盐台地沉积体系,可进一步划分为台地蒸发岩、局限台地、开阔台地、台地边缘生物礁滩和台地边缘斜坡5个相带。长兴期沿台地边缘发育了台地边缘礁滩;飞一段早期相对平静,沉积末期广旺海槽全部关闭;飞二段至飞三段早期主要为开阔台地沉积;飞三段晚期-飞四段演变为局限台地-台地蒸发岩相。飞二段浅滩与长兴期礁滩大致处于相同位置,未发生侧向迁移;飞三段台内浅滩的发育有明显的侧向迁移和垂向叠置的特征;从西南向东北方向,飞仙关组早期台地沉积区向陆棚沉积区迁移。

元坝地区长兴组储层溶蚀作用期次与机制研究

溶蚀作用是元坝地区长兴组碳酸盐岩储层形成的关键,本文通过区内长兴组岩芯及岩石薄片观察,岩石学特征与地球化学特征研究充分结合,认为元坝地区长兴组储层存在着三期溶蚀作用,不同期次溶蚀作用产物的岩石学特征和地球化学特征明显有别。第Ⅰ期溶蚀作用发生于同生期-成岩早期,成岩流体为海岸带大气降水,遵循高频层序界面、层序不整合界面、礁滩控制的大气水溶蚀作用机制;第Ⅱ期溶蚀作用发生于晚三叠世-中侏罗世的埋藏过程中,相当于中成岩早期阶段,成岩流体为上二叠统地层内部流体,溶蚀作用与烃源岩系有机质热演化释放的有机酸进入成岩流体有关;第Ⅲ期溶蚀作用发生于晚白垩世-古近纪的埋藏过程中,相当于成岩晚期阶段,成岩流体为长兴组地层内部来源或中下三叠统来源流体,或为深部热液流体,溶蚀作用遵循深埋藏条件下构造作用驱动的多类型溶蚀作用机制。第Ⅰ期、第Ⅱ期溶蚀作用形成的储渗空间对于液态原油运移进入长兴组聚集成藏(古油藏)具有重要意义,第Ⅲ期溶蚀作用形成的储渗空间对于现今天然气成藏具有重要意义。

川东北元坝地区长兴组流体包裹体特征及油气充注史

元坝气田长兴组生物礁(滩)相天然气藏是川东北地区近期勘探的热点。采用流体包裹体显微荧光技术和测温技术,结合IES(Integrated Exploration Systems)软件模拟的埋藏史和热演化史,对该区油气充注时间和成藏期次进行了研究。结果表明,元坝地区长兴组生物礁储集层大致经历了晚三叠世和晚三叠世-早白垩世2期原油充注。烃源岩生烃高峰与原油充注时间的高度匹配是元坝气田成藏的重要因素之一。

四川盆地元坝地区上三叠统须家河组的潮控河口湾与潮控三角洲沉积

通过盆地边缘地表剖面,以及元坝区岩芯的研究,发现须家河组并非长期以来人们普遍认定的陆相沉积,而是海岸系统产物。须二段属潮控河口湾环境,包括冲积河道、潮汐-河流水道、UFR沙坪、潮汐沙坝、泥坪和盐沼等相。须四段属潮控三角洲环境,包括三角洲平原河道、分流河口潮汐沙坝、三角洲前缘与前三角洲、泥坪与盐沼等相。这两种环境(沉积),都是海侵的产物,都是地史上的暂时现象。当其被充满时(海退),就变为潮坪-海岸平原环境,分别对应于须三段、须五段的细粒含煤序列。基于储层质量与原始沉积环境密切相关,划分了5类储层相。根据我们研究安岳地区须家河组的成功经验,提出了勘探建议。

四川盆地超深层天然气地球化学特征

对四川盆地38口井超深层(埋深大于6 000 m)天然气组分及其地球化学特征进行分析,以判明超深层天然气成因。四川盆地超深层天然气组分具如下特征:甲烷占绝对优势,含量最高达99.56%,平均86.67%;乙烷含量低,平均为0.13%;几乎没有丙、丁烷,为干气,属过成熟度气。硫化氢含量最高为25.21%,平均为5.45%;烷烃气碳同位素组成为:δ^(13)C_1值从-33.6‰变化至-26.7‰,δ^(13)C_2值从-32.9‰变化至-22.1‰,绝大部分没有倒转而主要为正碳同位素组成系列。烷烃气氢同位素组成为:δD_1值从-156‰变化至-113‰,少量井δD_2值从-103‰变化至-89‰。二氧化碳碳同位素组成为:δ^(13)C_(CO_2)值从-17.2‰变化至1.9‰,绝大部分在0±3‰范围。根据δ^(13)C_1-δ^(13)C_2-δ^(13)C_3鉴别图版,盆地超深层烷烃气除个别井外绝大部分为煤成气。根据二氧化碳成因鉴别图和δ^(13)C_(CO_2)值,判定除个别井外,超深层二氧化碳绝大部分为碳酸盐岩变质成因。龙岗气田和元坝气田超深层硫化氢为非生物还原型(热化学硫酸盐还原成因),双探号井的超深层硫化氢可能为裂解型(硫酸盐热裂解成因)。

川东北元坝区块中下侏罗统页岩油气地质分析

结合钻井、岩心、野外露头、测井等成果，从富含有机质页岩空间展布、地化特征、岩石矿物学、储集空间特征、孔渗性特征和地质力学性质等方面，对川东北元坝区块中下侏罗统页岩油气地质特征进行了综合研究。显著地质特征是：富有机质泥页岩主要发育于自流井组大安寨段和千佛崖组千一一二段，为浅湖一半深湖沉积，黑色泥页岩夹灰岩或砂岩。有机质较为发育，有机碳含量平均为1．14％，有机质类型以Ⅱ，型为主，镜质体反射率（R0）介于1．4％～1．6％之间，均处于凝析油-湿气的成熟-高成熟阶段。总体上，中下侏罗统页岩气构造简单、稳定，断裂不发育，保存条件良好，有利于烃类形成。大安寨段湖相页岩油气总体与北美E列eFord页岩气特征相似。大安寨段暗色泥页岩厚40～115m，孔隙类型丰富，发育水平缝和微裂缝，脆性矿物含量平均为52．7％．杨氏模量平均为37GPa．泊松比平均为0．30．有利于压裂形成网络裂缝。

元坝地区陆相地层钻井提速配套技术

四川盆地元坝气田天然气资源丰富,是中国石化的重点勘探开发区块,但钻速慢、钻井周期长是该区深井—超深井所面临的共同难题,该区域陆相侏罗系沙溪庙组—三叠系须家河组地层岩石致密、硬度高、可钻性差,此井段钻井周期约200d,占全井钻井周期的45%,严重制约了钻井提速提效。为此,开展了扭力冲击器配合PDC钻头、涡轮配合孕镶金刚石钻头、气体钻井等新技术应用试验,在试验效果的技术经济分析基础上,提出了延长气体钻井应用井段和深度的方案;对于不宜开展气体钻井的钻井液井段,如侏罗系自流井组中上部以浅地层或钻井液密度较低的地层推荐采用扭力冲击器提速,自流井组中下部—须家河组地层推荐应用涡轮钻具提速的方案。YB27-1H等11口井第三次开钻的314.1mm井段平均进尺1 885.29m,钻井周期缩短到166.18d,较前期平均值缩短34d。采用上述配套技术后,无论是钻井周期、日进尺均优于前期施工井,陆相地层提速提效取得了显著效果。

元坝地区须家河组砂岩成岩作用与孔隙演化

元坝地区上三叠统须家河组砂岩属于典型的低孔低渗型储层。通过显微镜下常规及铸体薄片鉴定、扫描电镜观察、X-衍射等手段,对研究区砂岩储层的成岩作用、孔隙演化及其对储集物性的影响进行了深入研究。研究区发育的成岩作用类型主要有压实作用、压溶作用、交代作用、胶结作用、溶蚀作用及破裂作用。其中破坏性成岩作用为压实压溶、硅质胶结和碳酸盐岩胶结作用;而绿泥石环边胶结、溶蚀和破裂作用则对储层起到了保护和改善作用。元坝地区须家河组砂岩目前已达中成岩阶段A期,一些地区已经达中成岩B期。储层经历强烈的成岩作用后原生孔隙基本被破坏,孔隙类型主要为次生孔隙并伴生裂缝。